Fabrics for outdoor uses have been known for many years, such as for patio furniture covers, covers for other products that are stored outside, and for a wide variety of other uses. Cotton duck and synthetic fiber fabrics, including those made of acrylics and polyolefins (such as polypropylene) have been particularly popular. However some or all of these fabrics have suffered from a number of deficiencies, such as (depending upon the particular prior art cover or other outdoor fabric) lack of color durability, lack of resistance to soiling so that the fabric does not retain a new and fresh appearance for a very long period of time, poor hand, less than desirable water and oil repellancy, and less structural strength than desired.
In most conventional outdoor use fabrics, finer yarn is used in the warp and heavier yarn used in the filling during the weaving process. The traditional thinking is that heavier yarn used in the filling means lower picks per inch need be used to obtain the fabric than with a finer yarn, and thus weaving costs are kept to a minimum. For example a conventional outdoor use woven fabric has a plain weave with finer yarn in the warp and heavier yarn in the filling, and with about 40% of the filling yarns equally exposed to both the back and the face of the fabric, and about 12% coring to the center of the fabric.
According to the present invention a method of making a polypropylene base fabric for outdoor use, and the fabric, and outdoor use product made from the fabric, are provided which have numerous advantages compared to prior art constructions. One of the most significant advantages of the fabric/product according to the invention is enhanced hand. While hand is difficult to measure quanitatively, it is one of the most easily recognized characteristics of a fabric by a consumer. While shear stiffness and flexural rigidity are not exactly equal to hand, the product according to the invention has improved shear stiffness and flexural rigidity, which are indicative of improved hand. The fabric according to the present invention has a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd.
The fabric according to the invention uses yarns comprising or consisting essentially of polypropylene, UV inhibitor for color fastness when exposed to sunlight, and a fluorochemical or fluoropolymer which causes the fabric to be inherently water repellent, and maintains water repellancy after abrasion. Because of the polymer mix utilized, and the controlled weaving, washing and drying conditions utilized in production, products according to the invention are softer and smoother than otherwise obtainable.
That is products according to the present invention have color durability, and resist fading from exposure to at least 500 hours of simulated sunlight. The products have a soft, comfortable soothing and smoother finish than comparable outdoor fabrics. The fabrics of the invention stay dryer than comparable fabrics that are surface treated with a fluorochemical water and oil repellancy treatment. The fabrics of the present invention continue to resist staining after wear abrasion such as with sandpaper. The fabrics of the present invention also tend to clean easily. Dirt can frequently be shaken from these fabrics, which exhibit much lower soiling than comparable fabrics. Finally, the fabrics of the invention dry more quickly than comparable fabrics making them resistant to mildew and tending to stay new and fresh appearing for much longer periods than comparable fabrics intended for outdoor use. However, an antimicrobial material may be added if desired.
Contrary to conventional thinking, the fabrics according to the invention are made with the filling yarns predominantly exposed to the face and with either the heavier yarn used in the warp direction and the finer yarn in the filling direction, or yarns of equal size or denier in the warp and filling directions. Therefore the invention uses a higher picks to warp ratio than comparable fabrics. Since it is the filling that is subjected to finishing processes, and fabrics according to the invention have not only more filling exposed but more filling picks inserted than comparable fabrics, the hand is necessarily superior.
According to one aspect of the present invention a method of making a polypropylene base fabric for outdoor use, using yarn comprising or consisting essentially of polypropylene, UV inhibitor, and a fluorochemical, is provided. The method comprises: (a) Weaving the yarn using heavier yarn in the warp direction and finer yarn in the filling direction, or yarns of substantially equal size or denier in the warp and filling directions, to produce a fabric having a face, a center, and a back, with at least 50% of the filling yarns exposed to the fabric face. (b) Washing the fabric to scour off spin finish on the yarns. And, (c) drying the washed fabric at a temperature below the softening point of polypropylene using air flow and tension control. The method may also comprise (d) making the fabric into an outdoor use product (such as a furniture cover), and (e) using the outdoor use product so that the face of the fabric faces the sun.
In the preferred embodiment, (a) is practiced to provide about 50-70%, preferably about 68-70%, of the filling yarns exposed to the fabric face, and about 6-10%, preferably about 8%, in the center, and about 20-40%, preferably about 22-24%, on the back. Typically (b) is practiced using water and detergent. Also typically (c) is practiced using a tenter frame, and at a temperature of between about 270-280 degrees F., and with an air flow of between about 4000-5100 cfm.
In the practice of the invention, typically (a)-(c) are practiced to produce a fabric having a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd. (a) through (c) are also typically practiced to produce a fabric having a weight between about 6-7 ounces per square yard, and to produce a fabric having a warp tear strength, pursuant to ASTM D117, of greater than 90, and a filling tear strength of greater than 26. That is (a)-(c) are practiced to produce a fabric having hand at least 10% better than if (a) were practiced using finer yarn in the warp and heavier yarn in the weft and about 44% of the filling yarns on each the face and back, and about 12% in the center.
According to another aspect of the present invention an outdoor object cover is made from a fabric produced from the method described above. The invention, according to another aspect, also comprises a woven fabric made of yarns consisting essentially of polypropylene, UV inhibitor, and fluorochemical air textured yarn, heavier yarn in the warp direction and finer yarn in the filling direction, or yarns of equal size or denier in the warp and filling directions, having a face, a center, and a back, with at least 50% of the filling yarns exposed to the fabric face. The woven fabric according to the invention preferably has about 68-70% of the filling yarns exposed to the fabric face, and about 8% in the center, and about 22-24% on the back; has a weight of between about 6-7 oz/sq. yd.; has a warp tear strength, pursuant to ASTM D117, of greater than 90, and a filling tear strength of greater than 26; and has a shear stiffness of comparable to less than 3.0 gf/cm*Degrees, and an overall flexural rigidity of comparable to less than 600, for a fabric having a weight of about 6.5 oz/sq. yd.
It is the primary object of the present invention to provide a highly advantageous outdoor use fabric in a simple, yet effective, manner. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.